'至于' (zhì yú) is a conjunction or preposition meaning 'as for', 'regarding', 'concerning', or 'when it comes to'. It introduces a new topic or shifts focus to a specific subject within a discussion. Though composed of two characters — 至 (zhì, 'to reach', 'up to') and 于 (yú, a classical preposition meaning 'at', 'in', or 'regarding') — the phrase functions as a fixed unit with no literal compositional meaning in modern usage. It often appears at the beginning of a clause or sentence to signal contrast, clarification, or topical transition.

This word is common in both spoken and written Chinese, especially when comparing or contrasting ideas, shifting attention between subjects, or introducing exceptions or qualifications. It frequently follows a preceding statement — for example, after mentioning one person or thing, '至于' introduces another. It carries a neutral-to-formal register and is widely used in daily conversation, essays, and news reports.